“This is what Cinderella would have worn on her wedding day!” said a bride, gushing over a Tiffany-blue ball gown on a recent episode of “Say Yes to the Dress: Atlanta.”

She had found her Prince Charming and spent years dreaming of being a princess on her wedding day. What could go wrong?

A lot, as we all know. The wedding may be the ending of most fairy tales, but it is supposed to be the beginning of a long partnership.

Since the 1970s, though, the percentage of Americans who eventually leave their marriage has been above 40 percent. The question is why.

When it comes to marriage, some things never change. That’s certainly one lesson from a recent survey of 4,000 ever-divorced adults between the ages of 18 and 60.

Researchers at the Austin Institute for the Study of Family and Culture used new data from the “Relationships in America” survey to find out why people got out of their marriages.

Sexual infidelity is still the most common reason for divorce. Nearly 37 percent of respondents cited their own infidelity or their spouse’s as a cause for the split.

However much our sexual mores may have loosened in recent years, it still seems that married couples expect their partners to remain faithful. If they didn’t, they would simply remain cohabiting couples — who are, by the way, much more likely to split.

Women are more likely to file for divorce, something that has been the case for well over a century now. Nor is this simply a matter of perspective: According to both men and women in the survey, women wanted the divorce more.

About 55 percent of women say they wanted the divorce more compared to only 20 percent of men who said they wanted it more. Given the complete revolution of the lives of women in the past 100 years, it’s remarkable this situation remains unchanged.

Indeed, no matter what place women have in the home or in the workplace, they still expect different things from a relationship. They are more likely to cite several reasons for divorce than men are.

And many of those reasons boil down to men “not meeting their emotional needs,” says Brad Wilcox of the National Marriage Project. Indeed, when you combine “spouse’s immaturity,” “emotional abuse” and “spouse unresponsive to needs,” these answers top even infidelity as a reason for divorce.

To some extent, this is a new phenomenon.

Kay Hymowitz, senior fellow at the Manhattan Institute, zeroes in on “spousal immaturity.” Her 2012 book, “Manning Up,” shows how 20- and 30-something men “often come across as aging frat boys, maladroit geeks or grubby slackers.”

And there seems to be no correlation, according to Dave Gordon, a researcher at the Austin Institute, between the age of the respondent and the likelihood he or she would cite “immaturity” as a reason for the end of the marriage.

So despite the fact that we are getting married later and later, on average, the issue of immaturity does not seem to be diminishing as a problem in our marriages. This may just be a men are from Mars, women are from Venus kind of issue.

As Wilcox notes, “women are more attuned to relationships. They put more effort into relationships. They are more acute and sensitive and reactive in every possible way when it comes to relationships. And they have more opinions and criticisms about their marriage and higher expectations for them.”

If we can’t get men to “man up” and we can’t get women to lower their expectations, what chance does the institution of marriage have? In the 1970s, when divorce skyrocketed, Wilcox says, many researchers expected that the upper classes would be worst hit.

The sexual revolution seemed to free them from the social strictures of marriage. Hope for the future of the American family rested on those middle and even lower classes in the heartland.

In fact, the exact opposite has proved true. Marriage is thriving among the wealthy and educated.

“Who would have thought elites would have devoted themselves maniacally to their children’s success?” asks Wilcox.

It seems as though marriage does well when it is a vehicle for something else — whether that’s making sure your children have food on the table or that they get into an Ivy League school.